Abstract

We present a real-time time-domain Doppler optical coherence tomography (OCT) system based on the zero-crossing method for velocity measurements of fluid flows with attainable velocities up to 10m/s. In the current implementation, one-dimensional and two-dimensional velocity profiles of fluid flows ranging from 1cm/s to more than 3m/s were obtained for both laminar and turbulent flows. The line rate was approximately 500Hz, and the images were treated in real time. This approach has the advantage of providing reliable velocity maps free from phase aliasing or other artifacts common to several OCT systems. The system is particularly well suited for investigating complex velocity profiles, especially in the presence of steep velocity gradients.

Laminar flow profiles within a cylindrical tube with light impinging from the right-hand side. (a) One raw A line superimposed with a theoretical parabola assuming a zero velocity at the tube walls and a maximum velocity in the center. The maximum speed was estimated by measuring the flow rate at the exit of the fluidic system. (b) Same theoretical profile with an averaged A line obtained with 20 raw A lines. (c) Two-dimensional image of the tube with a color-encoded velocity map.

Comparison of average velocities deduced from the measured flow rates and from the OCT Doppler profiles. The points in the middle were obtained with flows induced by gravity or by pumps and the four end points (at approximately ±2.2 and 2.35m/s) were obtained by using a syringe to inject the liquid into the tube.